ST. LOUIS — Facing the possibility of heading to Washington down 2-0 in a best-of-five series, the St. Louis Cardinals treated Monday like an elimination game.

The aggressor from the beginning in Game 2, the Cardinals jumped on the Nationals with a four-run second inning and continued to apply pressure, ensuring they wouldn’t let another winnable game slip away as they rolled to a 12-4 rout.

“If you go down 2-0, that means the margin for error is [gone],” said second baseman Daniel Descalso, who hit one of four St. Louis home runs. “Now it’s even, basically, it’s a clean slate. Now it’s a three-game series.”

The Cardinals seemed a step ahead the entire way, perhaps best exemplified by Pete Kozma’s hustle in going first-to-third on a Lance Lynn bunt back to reliever Craig Stammen in the fourth. And they kept on going, keeping runners in motion and working quality at-bats as they piled on the runs late.

“Those are the type of plays that sometimes get you going,” said Carlos Beltran, whose two monster homers didn’t hurt.

Added Descalso: “We sort of kept the momentum on our side.”

Garcia leaves with injury

Cardinals manager Mike Matheny’s decision to pinch-hit for starter Jaime Garcia while leading in the second inning raised some eyebrows at the time, but it turns out it wasn’t purely a tactical move.

Garcia’s arm was bothering him, Matheny revealed after the game, prompting the manager to turn to Lynn out of the bullpen.

“[Garcia] wasn’t feeling good and got to the point where he needed to say something,” Matheny said, “so we had to make a quick move.”

Garcia was sent for an MRI exam Monday night and Matheny said he would have further information Tuesday.

Garcia’s loss shouldn’t have any impact on the rest of the series, as Game 2 would have been his only start, but obviously it could have implications for the Cardinals if they advance.

Playoff format turns into positive development for Nationals

It was a quirk of the Major League Baseball postseason schedule this year that the Washington Nationals ended up here. That they, owners of the league’s best record, opened their first postseason series on the road.

But after a win in Game 1 of their National League Division Series with the Cardinals, the Nationals now face the attractive prospect of heading home to Washington in position to need only two wins, and possibly one depending on the result of Monday’s Game 2.

“With the first two on the road, you say to yourself, ‘If we get out of here with a split, we’re in good shape,’” said Nationals general manager Mike Rizzo after Sunday’s win. “Now you get greedy. You get the first one and you try to get the sweep here and go home even better.”

“It’s tough to start on the road,” first baseman Adam LaRoche said. “Game 1 in a short series like this is huge, I think, more than anything. Because now, for the Cardinals, since we won Game 1, this is kind of a must-win. You don’t want to get down two games in any series, but definitely not in a five-game.”

The five-game series puts less emphasis on where the games are played, Nationals third baseman Ryan Zimmerman said.

But Washington is acutely aware home field will be important should it advance to the NL Championship Series.

“If you want to win a series, you’re going to have to win a game on the road, whether you’re home field or not,” Zimmerman said. “I think obviously you don’t want to look ahead and we have a lot of work to do to win this series, but it really helps you next series.

“In a five-game series, anything can happen. If you start on the road [and] you split on the road, you’re looking pretty good going home. If you can somehow win both games, you’re looking really good going home. I think in a seven-game series it’s huge, which, because we won the regular season and all that, we’d have that next. But we’ve got to take business here, and this isn’t going to be an easy series to win.”

Game 3 time, TV announced

The first major league postseason game in the District in 79 years will be an old-fashioned weekday afternoon affair.

Game 3 of the NLDS will start at 1:07 p.m. Wednesday and will be televised on MLB Network with Bob Costas and Jim Kaat on the call.

There will be no over-the-air option for D.C.-area viewers who don’t get MLB Network, as there is with a Thursday night NFL Network game.

Limited standing-room-only tickets for Game 3 will go on sale at 9 a.m. Wednesday at the Nationals Park box office. Some single seats remain for purchase online and at the box office.

TV ratings all relative

Fittingly, Sunday’s TBS telecast of Game 1 of the NLDS drew the highest rating in the Washington market since baseball returned in 2005, an 8.4.

It would appear the District still has a ways to go as a baseball market compared to its neighbor to the north, though.

MLB said TBS pulled a 20.4 rating in Baltimore for Sunday’s Orioles-Yankees ALDS opener — despite the start of the game being delayed about 2 1/2 hours because of rain.

It should be noted that the Washington Redskins were still playing for about the first hour of the Nationals broadcast Sunday, while the Orioles-Yankees game had competition from Sunday Night Football and Game 2 of the Reds-Giants NLDS.